Drawings and design from live projects.

The garage forms the side structure to an existing single-storey property, and the client wished to convert it to habitable space. Three boreholes and trial pits were sunk to prove the ground and expose the neighbour's existing footings, finding coarse sands and gravels — likely river terrace deposits — over which traditional foundations could be safely formed.

Because new foundations sat directly against the boundary, a standard strip footing risked undermining the neighbouring wall. A stepped cantilever foundation was designed instead, using a deeper concrete section as a counterweight to keep the structure stable. The superstructure design covered the new flat roof, masonry leaf and a steel beam over the opening, all checked to Eurocode.

Trial pits revealed a blue-grey cohesive clay with peat inclusions and a perched groundwater table entering at around 1.5 m. The clay carries a medium volume-change potential, and the plot is ringed by willow, hawthorn and leylandii — all drivers of seasonal ground movement.

Founding depths were set using the NHBC tree-and-clay tables: up to 2.4 m where leylandii sit close to the works. The workshop was given pad foundations at depth with FND2 sulphate-resisting concrete, while the residential extensions were steered away from ground-bearing slabs toward suspended floors, to accommodate long-term heave as the ground recovers from removed trees.

Bi-fold doors are unforgiving of movement, so the supporting steel was sized for a deflection limit of under 1 mm rather than strength alone. A 178 UB with a welded bottom plate was detailed, with the connection arranged to bear cleanly onto the masonry and the secondary timber lantern trimmers framing in above. However, the design of bifold door beams needs to also take into account torsion (twist along the length of the beam), which occurs because the facing bickwork and door itself is "cantilevered" outside the centroid of the steel beam. Torsion in the beam though wont even develop without the ends of the beam being restrained against twist so the bottom plate has to extend out onto facing brickwork either end of the bifold door opening, welded to the beam and the plate has to be designed to take the full torsion each end as a buckling moment. The welds have to be designed for resisting the cantilevered loads but also need to be designed to limit heat induced buckling of the steel, as the weld itself is applied. This is done by designing the weld as a "hit and miss", taking into account deflection of the bottom plate between each leg of weld.

The package included the timber trimmer design for the roof lantern and the bolt, plate and weld specification for the steel — every member checked to the relevant Eurocode and issued as buildable details.